The present invention relates to ablation apparatus and methods, including those used in cardiac ablation.
Contraction or “beating” of the heart is controlled by electrical impulses generated at nodes within the heart and transmitted along conductive pathways extending within the wall of the heart. Certain diseases of the heart known as cardiac arrhythmias involve abnormal generation or conduction of the electrical impulses. One such arrhythmia is atrial fibrillation or “AF.” Certain cardiac arrhythmias can be treated by deliberately damaging the tissue along a path crossing a route of abnormal conduction, either by surgically cutting the tissue or applying energy or chemicals to the tissue, so as to form scar. The scar blocks the abnormal conduction. For example, in treatment of AF it has been proposed to ablate tissue in a partial or complete loop around a pulmonary vein within the vein itself near the ostium of the vein; within the ostium; or within the wall of the heart surrounding the ostium. It would be desirable to perform such ablation using a catheter-based device which can be advanced into the heart through the patient's circulatory system.
As described in certain embodiments of U.S. Pat. No. 6,635,034, the disclosure of which is hereby incorporated by reference herein, an expansible structure mounted at or near the distal end of a catheter is used as a reflector for directing and focusing ultrasonic waves from an ultrasonic transducer into a region of tissue to be ablated. Certain embodiments according to the '034 patent include an expansible structure incorporating a structural balloon which is inflated with a liquid and a reflector balloon inflated with a gas. The balloons share a common wall. The balloons are configured so that the common wall is generally in the form of a surface of revolution of a parabolic curve about a central axis. Because the liquid in the structural balloon and the gas in the reflector balloon have substantially different acoustic impedances, the interface between the balloons at the common wall is a nearly perfect reflector for ultrasonic waves. Ultrasonic waves are emitted from a small cylindrical transducer within the structural balloon, coaxial with the aforementioned reflector. These waves pass radially outwardly from the emitter to the reflector. The reflector redirects the ultrasonic waves and focuses them into a ring-like ablation region encircling the central axis of the emitter and balloons. This ablation region is just forward of the structural balloon. Thus, the ultrasonic waves will ablate tissue in a region encircling the central axis or forward-to-rearward axis of the balloon structure. This ring-like region is disposed at a known location relative to the balloon structure.
This arrangement can be used, for example, to treat atrial fibrillation by ablating a circular region of myocardial tissue encircling the ostium of a pulmonary vein. The ablated tissue forms a barrier to abnormal electrical impulses which can be transmitted along the pulmonary veins and, thus, isolates the myocardial tissue of the atrium from the abnormal impulses. To provide effective treatment in this mode of operation, the ring-like focal region should encircle the ostium and should lie in the myocardial tissue of the heart wall.
It is desirable to maintain the expansible structure in a predetermined configuration and, in particular, to keep the distal end of the structural balloon coaxial with the proximal end of the structural balloon and with the reflector and transducer. The expansible structure may be provided with a distal engagement element mechanically connected to the distal end of the structural balloon and with a proximal engagement element mechanically connected to the transducer and to the proximal end of the structural balloon. These elements engage one another to reinforce the expansible structure when the structural balloon is inflated, but at least partially disengage from one another when the structural balloon is deflated, so that the deflated, collapsed structure is flexible and can be threaded through the vascular system into the heart. Additionally, the expansible structure desirably is provided with a bore connected to a lumen of the catheter so that the expansible structure and the catheter cooperative define a continuous passageway extending from adjacent the proximal end of the catheter to the distal side of the expansible structure. This passageway can be used to introduce an X-ray or other contrast agent during the procedure, so the position of the expansible structure relative to anatomical features of the heart may be determined by imaging. Moreover, the catheter desirably is steerable so that a portion of the catheter adjacent the distal end can be selectively bent by the physician, so as to reposition the expansible structure. These features are further described in certain embodiments of co-pending, commonly assigned U.S. patent application Ser. No. 10/783,310, filed Feb. 20, 2004 (“the '310 application”); PCT International Application No. PCT/US04/05197; and U.S. Published Patent Application 20040054362A1, filed Sep. 16, 2002; as well as in co-pending, commonly assigned U.S. patent application Ser. No. 10/635,170, filed Aug. 6, 2003 and PCT International Application No. PCT/US03/28578, filed Sep. 12, 2003. The disclosures of all of the aforementioned applications and publications are hereby incorporated by reference herein.
Despite all of these advances in the art, still further improvement would be desirable. In particular, it would be desirable to provide apparatus and methods for ablation which allow the physician to acquire information about anatomical structures of the heart and surrounding tissues. Such information can be used in positioning the ablation device. For example, where structures other than myocardial tissue must remain intact after the ablation procedure, such information allows the physician to position the ablation device so as to avoid ablating these structures. Conversely, where structures such as certain nerve bundles are to be ablated, such information allows the physician to more accurately position the ablation device for greater certainty of ablating these structures.